The CO2 emissions manipulations, which translate into higher than stated fuel consumption, have been uncovered about six weeks after the US Environmental Protection Agency exposed Volkswagen for using software to cheat in nitrogen emission tests.

In the wake of the revelations, the UK has launched an inquiry into the national system of approving vehicles and their emissions levels.

The investigation will also address one of the major complaints that have emerged in recent weeks regarding the difference between laboratory and real-world emissions levels.

"The gap between emissions detected in test conditions and those detected in the real world (is) significant," committee chairwoman Louise Ellman said on Monday. "The testing procedure is clearly inadequate."

Critics, including some members of the European parliament, have also focused on the current system of different national bodies holding powers to approve vehicles, with calls for a single European entity.

Ellman said compromise plans agreed by EU countries to allow vehicles to carry on emitting more than twice the agreed pollution limits had been ‘criticised for giving too much leeway to motor manufacturers’.

"It is essential to examine these allegations and to ensure that the government and EU take action to restore public confidence," she said.